1. Field of the Disclosure
The present disclosure relates to a communication module capable of concurrently performing wireless communications in which different frequency bands are used.
2. Description of the Related Art
Mobile devices that have been widely used in recent years have communication functions based on various communication methods such as in wireless local area network (LAN) communication and Bluetooth (registered trademark) communication. Japanese Unexamined Patent Application Publication No. 2010-16732 describes a wireless communication device capable of performing 2.4-GHz communications over a wireless LAN and a Bluetooth (registered trademark) network at the same time. With this wireless communication device, a single antenna is shared by two communication methods, so the number of parts is smaller than when an independent antenna is used for each of the two communication methods.
Besides the 2.4-GHz band, the 5-GHz band can be used on wireless LANs. Recent mobile devices are becoming ready not only for a 2.4-GHz wireless LAN and Bluetooth (registered trademark) network but also for a relatively high-speed wireless LAN in the 5-GHz band.
When one device performs wireless communications in different frequency bands, an antenna is usually used for each frequency band. To reduce the number of parts, however, it is desirable to share a single antenna between wireless communications in two frequency bands as in the wireless communication device described in Japanese Unexamined Patent Application Publication No. 2010-16732.
Part of the frequency band used by a 5-GHz wireless LAN overlaps frequency bands used by weather radars and the like. To prevent effects on the operations of these radars, there is an obligation to use a frequency switching function called dynamic frequency selection (DFS). DFS monitors whether there is a radar radio wave when a frequency channel starts to be used or while it is being used. If a radar radio wave is detected, transmission of radio waves at the frequency channel is prohibited and the frequency channel is switched to. On a 5-GHz wireless LAN, therefore, DFS regularly performs a reception operation for radar radio wave monitoring. If this reception operation by DFS is performed by using the same antenna as used in 2.4-GHz wireless LAN communication or Bluetooth (registered trademark) communication, a 2.4-GHz transmission signal may enter a 5-GHz reception circuit, which may prevent a normal reception operation. If, for example, a large signal in the 2.4-GHz band enters a 5-GHz reception circuit, the signal level is saturated in a circuit element in an amplifier at the first stage, in which case, even if filtering or other processing is performed in a circuit at a later stage, a normal 5-GHz reception signal cannot be obtained. To avoid this problem, when the same antenna is used to perform 2.4-GHz wireless communication (wireless LAN communication or Bluetooth communication) and 5-GHz wireless communication (wireless LAN communication) at the same time, it is necessary to provide a filter that attenuates the 2.4-GHz signal transmitted from the antenna to a 5-GHz communication circuit.
However, it is not determined whether a device that performs 2.4-GHz wireless communication (wireless LAN communication or Bluetooth communication) and 5-GHz wireless communication (wireless LAN communication) at the same time uses a shared antenna or independent antennas. Therefore, communication modules are preferably structured so as to be easily applicable to both types of devices.